1. Field of the Invention
The present invention relates to a continuous steel casting mold whose walls are composed of a base member of copper alloy provided with cooling ducts and of a working coating provided on the base member.
2. Description of the Related Art
The most important requirements made of continuous steel casting molds are good heat conductivity, resistance to wear and dimensional stability. In order to meet these requirements, continuous steel casting molds have been developed which have shaping walls of pure copper, copper alloy and of copper coated with chromium and nickel.
EP-A-0 383 934 discloses continuous steel casting molds whose walls which consist of copper or copper alloy have on the working side a coating of nickel alloy. In order to flatten the differences in degrees of hardness between the copper wall and the very hard nickel alloy layer and for improving the connection, an intermediate layer of nickel is arranged between the copper wall and the layer of nickel alloy.
In continuous casting plants for casting steel strips developed more recently, the molds used in the plants are subjected to significantly more problems due to wear, stress-related distortion and the formation of cracks. This is because the casting rates are higher and the mold cavities have a complex shape.
The invention starts from the finding that local high stress peaks at the surface lead to damage, particularly to the formation of cracks, because of the fact that expansion is prevented. The tendency to form cracks and the spreading of cracks is increased by the formation of brass which is due to diffusion of zinc into the working surface.